Sub-block based use of transform skip mode

ABSTRACT

Devices, systems and methods for lossless coding for visual media coding are described. An exemplary method for video processing includes determining, at a sub-block level of a current video block comprising multiple sub-blocks, whether a coding mode is enabled for representing a corresponding sub-block in a bitstream representation, where, for a given sub-block with the coding mode enabled, the given sub-block is represented in the coded representation without applying a forward transform or the given sub-block is reconstructed from the coded representation without applying an inverse transform, and performing, based on the determining, a conversion between the current video block of a video and the bitstream representation of the video.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 17/529,533 filed on Nov. 18, 2021, which is a continuation of International Patent Application No. PCT/CN2020/091543 filed on May 21, 2020, which claims the priority to and benefits of International Patent Application PCT/CN2019/087986 filed on May 22, 2019. All the aforementioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to video coding methods, devices, and systems.

BACKGROUND

In spite of the advances in video compression, digital video still accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, and specifically, to lossless coding for visual media coding. The described methods may be applied to both the existing video coding standards (e.g., high efficiency video coding (HEVC)) and future video coding standards (e.g., versatile video coding (VVC)) or video codecs.

In one representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes determining, at a sub-block level of a current video block comprising multiple sub-blocks, whether a coding mode is enabled for representing a corresponding sub-block in a bitstream representation, wherein, for a given sub-block with the coding mode enabled, the given sub-block is represented in the coded representation without applying a forward transform or the given sub-block is reconstructed from the coded representation without applying an inverse transform; and performing, based on the determining, a conversion between the current video block of a video and the bitstream representation of the video.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes determining that a conversion between a current video block of a video and a coded representation of the video is based on a first coding mode in which a lossless coding technique is used for representing the current video block in the coded representation; and performing the conversion, based at least on the determining, by disabling a luma mapping with chroma scaling (LMCS) process, wherein the disabling the LMCS process disables a performance of switching between samples in a reshaped domain and an original domain for the current video block in a case that the current video block is from a luma component or disables a scaling of a chroma residual of the current video block in case that the current video block is from a chroma component.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes performing a conversion between a current video block of a video and a bitstream representation of the video, wherein the bitstream representation conforms to a first format rule that specifies an order of occurrence of a first syntax element of a transquant bypass mode and one or more syntax elements of quantization parameters, wherein the bitstream representation conforms to a second format rule that specifies whether the first syntax elements and the one or more syntax elements are included in the coded representation, and wherein, in the transquant bypass mode, a transform and quantization process is not applied to the current video block during encoding or an inverse transform and an inverse quantization is not used during decoding of the coded representation for the current video block.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes performing a conversion between a current video block of a video segment of a video and a bitstream representation of a video, wherein the conversion is in conformance with a format rule that specifies an applicability relationship between an applicability of a transquant bypass mode and a luma mapped chroma scaling (LMCS) mode to the conversion of the current video block, wherein the format rule further specifies a syntax structure at the video segment level indicative of the applicability relationship, wherein, in the transquant bypass mode, a transform and quantization process is not used on the current video block, and wherein the LMCS mode comprises a performance of switching between samples in a reshaped domain and an original domain for the current video block in case that the current video block is from a luma component or a scaling of a chroma residual of the current video block in case that the current video block is from a chroma component.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes performing a conversion between a current video block of a video and a bitstream representation of the video according to a first rule and a second rule, wherein the first rule specifies whether an inverse reshaping process is used during the conversion for generating decoded pixel values of the current video block by converting from a reshaped domain to an original domain, and wherein the second rule specifies an order in which the inverse reshaping process and a loop filtering process are applied for reconstruction of the current video block.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes configuring, for a current video block comprising a plurality of color components, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is signalled separately in the bitstream representation for at least two color components of the plurality of color components, and performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block.

In another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes making a decision, based on a characteristic of a current video block, regarding an enablement of a mode that skips an application of a transform and quantization process on the current video block, and performing, based on the decision, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes making a decision, based on at least one dimension of a current video block, regarding an enablement of a first mode that skips an application of a transform and quantization process on the current video block and a second mode that does not apply a transform to the current video block, and performing, based on the decision, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes determining that a current video block is coded using a first mode and a second mode that skips an application of a transform and quantization process on the current video block, and performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes configuring, for a current video block, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is signalled in the bitstream representation before signalling syntax elements related to one or more multiple transform related coding tools, and performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes determining that a current video block is coded using a mode that skips an application of a transform and quantization process on the current video block, and disabling, based on the determining and as part of performing a conversion between the current video block and a bitstream representation of the current video block, a filtering method.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes determining that a current video block is coded using a mode that skips an application of a transform and quantization process on the current video block, and disabling, based on the determining and as part of performing a conversion between the current video block and a bitstream representation of the current video block, an in-loop reshaping (ILR) process for (i) a current picture comprising the current video block or (ii) a portion of the current picture.

In yet another representative aspect, the disclosed embodiments may be used to provide a method for video processing. This method includes configuring, for a current video block, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is selectively signalled in the bitstream representation after signalling one or more indications of quantization parameters; and performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block.

In yet another representative aspect, the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.

In yet another representative aspect, a device that is configured or operable to perform the above-described method is disclosed. The device may include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus may implement a method as described herein.

The above and other aspects and features of the disclosed embodiments are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an example encoder.

FIG. 2 shows an example of 67 intra prediction modes.

FIGS. 3A-3D show examples of samples used by a position dependent intra prediction combination (PDPC) method applied to diagonal and adjacent angular intra modes.

FIG. 4 shows an example of four reference lines neighboring a prediction block.

FIG. 5 shows an example of divisions of 4×8 and 8×4 blocks.

FIG. 6 shows an example of divisions all blocks except 4×8, 8×4 and 4×4.

FIG. 7 shows an example of affine linear weighted intra prediction (ALWIP) for 4×4 blocks.

FIG. 8 shows an example of ALWIP for 8×8 blocks.

FIG. 9 shows an example of ALWIP for 8×4 blocks.

FIG. 10 shows an example of ALWIP for 16×16 blocks.

FIG. 11 shows an example of a secondary transform in Joint Exploration Model (JEM).

FIG. 12 shows an example of the proposed reduced secondary transform (RST).

FIG. 13 shows an example of sub-block transform modes SBT-V and SBT-H.

FIG. 14 shows a flowchart of a decoding flow with reshaping.

FIGS. 15A-15G show flowcharts of example methods for video processing.

FIG. 16 is a block diagram of an example of a hardware platform for implementing a visual media decoding or a visual media encoding embodiment described in the present disclosure.

FIG. 17 is a block diagram that illustrates an example video coding system that may utilize the embodiments of this disclosure.

FIG. 18 is a block diagram illustrating an example of video encoder.

FIG. 19 is a block diagram illustrating an example of video decoder.

FIG. 20 is a block diagram showing an example video processing system in which various embodiments disclosed herein may be implemented.

FIGS. 21-25 show flowcharts of example methods for video processing.

DETAILED DESCRIPTION

Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H.265) and future standards to improve compression performance. Section headings are used in the present disclosure to improve readability of the description and do not in any way limit the discussion or the embodiments to the respective sections only.

2 Video Coding Introduction

Due to the increasing demand of higher resolution video, video coding methods and techniques are ubiquitous in modern technology. Video codecs typically include an electronic circuit or software that compresses or decompresses digital video, and are continually being improved to provide higher coding efficiency. A video codec converts uncompressed video to a compressed format or vice versa. There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency). The compressed format usually conforms to a standard video compression specification, e.g., the high efficiency video coding (HEVC) standard (also known as H.265 or MPEG-H Part 2) [1], the versatile video coding (VVC) standard to be finalized, or other current and/or future video coding standards.

Video coding standards have evolved primarily through the development of the well-known International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) and International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) standards. The ITU-T produced H.261 and H.263, ISO/IEC produced Moving Picture Experts Group (MPEG)-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (JVET) was founded by Video Coding Experts Group (VCEG) and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM) [3][4]. In April 2018, the JVET between VCEG (Q6/16) and ISO/IEC JTC1 SC29/WG11 (MPEG) was created to work on the VVC standard targeting a 50% bitrate reduction compared to HEVC.

2.1 Coding Flow of a Typical Video Codec

FIG. 1 shows an example of encoder block diagram of VVC, which contains three in-loop filtering blocks: deblocking filter (DF), sample adaptive offset (SAO) and adaptive loop filter (ALF). Unlike DF, which uses predefined filters, SAO and ALF utilize the original samples of the current picture to reduce the mean square errors between the original samples and the reconstructed samples by adding an offset and by applying a finite impulse response (FIR) filter, respectively, with coded side information signalling the offsets and filter coefficients. ALF is located at the last processing stage of each picture and can be regarded as a tool trying to catch and fix artifacts created by the previous stages.

2.2 Intra Mode Coding with 67 Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, the number of directional intra modes is extended from 33, as used in HEVC, to 65. The additional directional modes are depicted as dotted arrows in FIG. 2 , and the planar and DC modes remain the same. These denser directional intra prediction modes apply for all block sizes and for both luma and chroma intra predictions.

Conventional angular intra prediction directions are defined from 45 degrees to −135 degrees in clockwise direction as shown in FIG. 2 . In VVC Test Model (VTM)2, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks. The replaced modes are signalled using the original method and remapped to the indexes of wide angular modes after parsing. The total number of intra prediction modes is unchanged, i.e., 67, and the intra mode coding is unchanged.

In the HEVC, every intra-coded block has a square shape and the length of each of its side is a power of 2. Thus, no division operations are required to generate an intra-predictor using DC mode. In VVC, blocks can have a rectangular shape that necessitates the use of a division operation per block in the general case. To avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks.

2.2.1 Position Dependent Intra Prediction Combination (PDPC)

In the VTM2, the results of intra prediction of planar mode are further modified by a position dependent intra prediction combination (PDPC) method. PDPC is an intra prediction method which invokes a combination of the un-filtered boundary reference samples and HEVC style intra prediction with filtered boundary reference samples. PDPC is applied to the following intra modes without signalling: planar, DC, horizontal, vertical, bottom-left angular mode and its eight adjacent angular modes, and top-right angular mode and its eight adjacent angular modes.

The prediction sample pred(x,y) is predicted using an intra prediction mode (DC, planar, angular) and a linear combination of reference samples according to the Equation as follows:

pred(x,y)=(wL×R _(−1,y) +wT×R _(x,−1) −wTL×R _(−1,−1)+(64−wL−wT+wTL)×pred(x,y)+32)>>6

Herein, R_(x,−1), R_(−1,y) represent the reference samples located at the top and left of current sample (x, y), respectively, and R_(−1,−1) represents the reference sample located at the top-left corner of the current block.

If PDPC is applied to DC, planar, horizontal, and vertical intra modes, additional boundary filters are not needed, as required in the case of HEVC DC mode boundary filter or horizontal/vertical mode edge filters.

FIGS. 3A-3D illustrate the definition of reference samples (R_(x,−1), R_(−1,y) and R_(−1,−1)) for PDPC applied over various prediction modes. The prediction sample pred (x′, y′) is located at (x′, y′) within the prediction block. The coordinate x of the reference sample R_(x,−1) is given by: x=x′+y′+1, and the coordinate y of the reference sample R_(−1,y) is similarly given by: y=x′+y′+1. The PDPC weights are dependent on prediction modes and are shown in Table 1.

TABLE 1 Example of PDPC weights according to prediction modes Prediction modes wT wL wTL Diagonal top-right 16 >> ( ( y′<<1 ) >> shift) 16 >> ( ( x′<<1 ) >> shift) 0 Diagonal bottom-left 16 >> ( ( y′<<1 ) >> shift ) 16 >> ( ( x′<<1 ) >> shift ) 0 Adjacent diagonal top-right 32 >> ( ( y′<<1 ) >> shift ) 0 0 Adjacent diagonal bottom-left 0 32 >> ( ( x′<<1 ) >> shift ) 0

2.3 Multiple Reference Line (MRL)

Multiple reference line (MRL) intra prediction uses more reference lines for intra prediction. In FIG. 4 , an example of 4 reference lines is depicted, where the samples of segments A and F are not fetched from reconstructed neighboring samples but padded with the closest samples from Segment B and E, respectively. HEVC intra-picture prediction uses the nearest reference line (i.e., reference line 0). In MRL, 2 additional lines (reference line 1 and reference line 3) are used.

The index of selected reference line (mrl_idx) is signalled and used to generate intra predictor. For reference line index, which is greater than 0, only include additional reference line modes in MPM list and only signal MPM index without remaining mode. The reference line index is signalled before intra prediction modes, and planar and DC modes are excluded from intra prediction modes in case a nonzero reference line index is signalled.

MRL is disabled for the first line of blocks inside a coding tree unit (CTU) to prevent using extended reference samples outside the current CTU line. Also, PDPC is disabled when additional line is used.

2.4 Intra Subblock Partitioning (ISP)

In JVET-M0102, ISP is proposed, which divides luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size dimensions, as shown in Table 2. FIG. 5 and FIG. 6 show examples of the two possibilities. All sub-partitions fulfill the condition of having at least 16 samples. For block sizes, 4×N or N×4 (with N>8), if allowed, the 1×N or N×1 sub-partition may exist.

TABLE 2 Number of sub-partitions depending on the block size (denoted maximum transform size by maxTBSize) Number of Sub- Splitting direction Block Size Partitions N/A minimum transform size Not divided 4 × 8: horizontal 4 × 8 and 8 × 4 2 8 × 4: vertical Signaled If neither 4 × 8 nor 8 × 4, and 4 W <= maxTBSize and H <= maxTBSize Horizontal If not above cases and H > maxTBSize 4 Vertical If not above cases and H > maxTBSize 4

For each of these sub-partitions, a residual signal is generated by entropy decoding the coefficients sent by the encoder and then inverse quantizing and inverse transforming them. Then, the sub-partition is intra predicted and finally the corresponding reconstructed samples are obtained by adding the residual signal to the prediction signal. Therefore, the reconstructed values of each sub-partition will be available to generate the prediction of the next one, which will repeat the process and so on. All sub-partitions share the same intra mode.

TABLE 3 Specification of trTypeHor and trTypeVer depending on predModeIntra predModeIntra trTypeHor trTypeVer INTRA_PLANAR, ( nTbW >= 4 && ( nTbH >= 4 && INTRA_ANGULAR31, nTbW <= 16 ) ? nTbH <= 16 ) ? INTRA_ANGULAR32, DST-VII : DCT-II DST-VII : DCT-II INTRA_ANGULAR34, INTRA_ANGULAR36, INTRA_ANGULAR37 INTRA_ANGULAR33, DCT-II DCT-II INTRA_ANGULAR35 INTRA_ANGULAR2, ( nTbW >= 4 && DCT-II INTRA_ANGULAR4, . . . , nTbW <= 16 ) ? INTRA_ANGULAR28, DST-VII : DCT-II INTRA_ANGULAR30, INTRA_ANGULAR39, INTRA_ANGULAR41, . . . , INTRA_ANGULAR63, INTRA_ ANGULAR65 INTRA_ANGULAR3, DCT-II ( nTbH >= 4 && INTRA_ANGULAR5, . . . , nTbH <= 16 ) ? INTRA_ANGULAR27, DST-VII : DCT-II INTRA_ANGULAR29, INTRA_ANGULAR38, INTRA_ANGULAR40, . . . , INTRA_ANGULAR64, INTRA_ANGULAR66

2.5 Affine Linear Weighted Ultra Prediction (ALWIP or Matrix-Based Ultra Prediction)

Affine linear weighted intra prediction (ALWIP, which may also be referred to as matrix based intra prediction (MIP)) is proposed in JVET-N0217.

2.5.1 Generation of the Reduced Prediction Signal by Matrix Vector Multiplication

The neighboring reference samples are first down-sampled via averaging to generate the reduced reference signal bdry_(red). Then, the reduced prediction signal pred_(red) is computed by calculating a matrix vector product and adding an offset:

pred_(red) =A·bdry_(red) +b

Here, A is a matrix that has Wre_(d) Hre_(d) rows and 4 columns if W=H=4 and 8 columns in all other cases. b is a vector of size Wre_(d)-Hre_(d).

2.5.2 Illustration of the Entire ALWIP Process

The entire process of averaging, matrix vector multiplication and linear interpolation is illustrated for different shapes in FIGS. 7-10 . Note, that the remaining shapes are treated as in one of the depicted cases.

FIG. 7 shows an example of ALWIP for 4×4 blocks. 1. Given a 4×4 block, ALWIP takes two averages along each axis of the boundary. The resulting four input samples enter the matrix vector multiplication. The matrices are taken from the set S₀. After adding an offset, this yields the 16 final prediction samples. Linear interpolation is not necessary for generating the prediction signal. Thus, a total of (4·16)/(4·4)=4 multiplications per sample are performed.

FIG. 8 shows an example of ALWIP for 8×8 blocks. 2. Given an 8×8 block, ALWIP takes four averages along each axis of the boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S₁. This yields 16 samples on the odd positions of the prediction block. Thus, a total of (8·16)/(8·8)=2 multiplications per sample are performed. After adding an offset, these samples are interpolated vertically by using the reduced top boundary. Horizontal interpolation follows by using the original left boundary.

FIG. 9 shows an example of ALWIP for 8×4 blocks. 3. Given an 8×4 block, ALWIP takes four averages along the horizontal axis of the boundary and the four original boundary values on the left boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S₁. This yields 16 samples on the odd horizontal and each vertical positions of the prediction block. Thus, a total of (8·16)/(8·4)=4 multiplications per sample are performed. After adding an offset, these samples are interpolated horizontally by using the original left boundary.

FIG. 10 shows an example of ALWIP for 16×16 blocks. 4. Given a 16×16 block, ALWIP takes four averages along each axis of the boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S₂. This yields 64 samples on the odd positions of the prediction block. Thus, a total of (8·64)/(16·16)=2 multiplications per sample are performed. After adding an offset, these samples are interpolated vertically by using eight averages of the top boundary. Horizontal interpolation follows by using the original left boundary. The interpolation process, in this case, does not add any multiplications. Therefore, totally, two multiplications per sample are required to calculate ALWIP prediction.

For larger shapes, the procedure is essentially the same and it is easy to check that the number of multiplications per sample is less than four.

For W×8 blocks with W>8, only horizontal interpolation is necessary as the samples are given at the odd horizontal and each vertical positions.

Finally, for W×4 blocks with W>8, let A_(k) be the matrix that arises by leaving out every row that corresponds to an odd entry along the horizontal axis of the downsampled block. Thus, the output size is 32 and again, only horizontal interpolation remains to be performed. The transposed cases are treated accordingly.

2.6 Multiple Transform Set (MTS) in VVC 2.6.1 Explicit MTS

In VTM4, large block-size transforms, up to 64×64 in size, are enabled, which is primarily useful for higher resolution video, e.g., 1080p and 4K sequences. High frequency transform coefficients are zeroed out for the transform blocks with size (width or height, or both width and height) equal to 64, so that only the lower-frequency coefficients are retained. For example, for an M×N transform block, with M as the block width and N as the block height, when M is equal to 64, only the left 32 columns of transform coefficients are kept. Similarly, when N is equal to 64, only the top 32 rows of transform coefficients are kept. When transform skip mode is used for a large block, the entire block is used without zeroing out any values.

In addition to discrete cosine transform (DCT)-II which has been employed in HEVC, a MTS scheme is used for residual coding both inter and intra coded blocks. It uses multiple selected transforms from the DCT8/DST7. The newly introduced transform matrices are DST-VII and DCT-VIII. The Table 4 below shows the basis functions of the selected DST/DCT.

TABLE 4 Basis functions of transform matrices used in VVC Transform Type Basis function T_(i)(j), i, j = 0, 1, . . . , N − 1 DCT-II ${T_{i}(j)} = {{\omega_{0} \cdot \sqrt{\frac{2}{N}} \cdot \cos}\left( \frac{\pi \cdot i \cdot \left( {{2j} + 1} \right)}{2N} \right)}$ ${{where}\omega_{0}} = \left\{ \begin{matrix} \sqrt{\frac{2}{N}} & {i = 0} \\ 1 & {i \neq 0} \end{matrix} \right.$ DCT-VIII ${T_{i}(j)} = {{\sqrt{\frac{4}{{2N} + 1}} \cdot \cos}\left( \frac{\pi \cdot \left( {{2i} + 1} \right) \cdot \left( {{2j} + 1} \right)}{{4N} + 2} \right)}$ DST-VII ${T_{i}(j)} = {{\sqrt{\frac{4}{{2N} + 1}} \cdot \sin}\left( \frac{\pi \cdot \left( {{2i} + 1} \right) \cdot \left( {j + 1} \right)}{{2N} + 1} \right)}$

In order to keep the orthogonality of the transform matrix, the transform matrices are quantized more accurately than the transform matrices in HEVC. To keep the intermediate values of the transformed coefficients within the 16-bit range, after horizontal and after vertical transform, all the coefficients are to have 10 bits.

In order to control MTS scheme, separate enabling flags are specified at SPS level for intra and inter, respectively. When MTS is enabled at SPS, a coding unit (CU) level flag is signalled to indicate whether MTS is applied or not. Here, MTS is applied only for luma. The MTS CU level flag is signalled when the following conditions are satisfied.

-   -   Both width and height less than or equal to 32     -   Coded block flag (CBF) flag is equal to one

If MTS CU flag is equal to zero, then DCT2 is applied in both directions. However, if MTS CU flag is equal to one, then two other flags are additionally signalled to indicate the transform type for the horizontal and vertical directions, respectively. Transform and signalling mapping table as shown in Table 5. When it comes to transform matrix precision, 8-bit primary transform cores are used. Therefore, all the transform cores used in HEVC are kept as the same, including 4-point DCT-2 and DST-7, 8-point, 16-point and 32-point DCT-2. Also, other transform cores including 64-point DCT-2, 4-point DCT-8, 8-point, 16-point, 32-point DST-7 and DCT-8, use 8-bit primary transform cores.

TABLE 5 Mapping of decoded value of tu_mts_idx and corresponding transform matrices for the horizontal and vertical directions. Bin string of Intra/inter tu_mts_idx tu_mts_idx Horizontal Vertical 0 0 DCT2 1 0 1 DST7 DST7 1 1 0 2 DCT8 DST7 1 1 1 0 3 DST7 DCT8 1 1 1 1 4 DCT8 DCT8

To reduce the complexity of large size DST-7 and DCT-8, high-frequency transform coefficients are zeroed out for the DST-7 and DCT-8 blocks with size (width or height, or both width and height) equal to 32. Only the coefficients within the 16×16 lower-frequency region are retained.

In addition to the cases wherein different transforms are applied, VVC also supports a mode called transform skip (TS) which is like the concept of TS in the HEVC. TS is treated as a special case of MTS.

2.6.1.1 Syntax and Semantics

MTS index may be signalled in the bitstream and such a design is called explicit MTS. In addition, an alternative way which directly derives the matrix according to transform block sizes is also supported, referred to as implicit MTS.

For the explicit MTS, it supports all coded modes. While for the implicit MTS, only intra mode is supported.

7.3.2.4 Picture Parameter Set RBSP Syntax

Descriptor pic_parameter_set_rbsp( ) {  pps_pic_parameter_set_id ue(v)  pps_seq_parameter_set_id ue(v)  output_flag_present_flag u(1)  single_tile_in_pic_flag u(1) ...  init_qp_minus26 se(v)  transform_skip_enabled_flag u(1)  if( transform_skip_enabled_flag )   log2_transform_skip_max_size_minus2 ue(v)  cu_qp_delta_enabled_flag u(1)  if( cu_qp_delta_enabled_flag )   cu_qp_delta_subdiv ue(v)  pps_cb_qp_offset se(v)  pps_cr_qp_offset se(v)  pps_slice_chroma_qp_offsets_present_flag u(1)  weighted_pred_flag u(1)  weighted_bipred_flag u(1)  deblocking_filter_control_present_flag u(1)  if( deblocking_filter_control_present_flag ) {   deblocking_filter_override_present_flag u(1)   pps_deblocking_filter_disabled_flag u(1)   if( !pps_deblocking_filter_disabled_flag ) {    pps_beta_offset_div2 se(v)    pps_tc_offset_div2 se(v)   }  }  pps_loop_filter_across_virtual_boundaries_disabled_flag u(1)  if( pps_loop_filter_across_virtual_boundaries_disabled_flag ) {   pps_num_ver_virtual_boundaries u(2)   for( i = 0; i < pps_num_ver_virtual_boundaries; i++ )    pps_virtual_boundaries_pos_x[ i ] u(v)   pps_num_hor_virtual_boundaries u(2)   for( i = 0; i < pps_num_hor_virtual_boundaries; i++ )    pps_virtual_boundaries_pos_y[ i ] u(v)  }  pps_extension_flag u(1)  if( pps_extension_flag )   while( more_rbsp_data( ) )    pps_extension_data_flag u(1)  rbsp_trailing_bits( ) }

7.3.7.10 Transform Unit Syntax

Descriptor transform_unit( x0, y0, tbWidth, tbHeight, treeType, subTuIndex ) { ...  if( ( tu_cbf_luma[ x0 ][ y0 ] | | tu_cbf_cb[ x0 ][ y0 ] | | tu_cbf_cr[ x0 ][ y0 ] ) &&   treeType != DUAL_TREE_CHROMA ) {   if( cu_qp_delta_enabled_flag && !IsCuQpDeltaCoded ) {    cu_qp_delta_abs ae(v)    if( cu_qp_delta_abs )     cu_qp_delta_sign_flag ae(v)   }  }  if( tu_cbf_luma[ x0 ][ y0 ] && treeType != DUAL_TREE_CHROMA   && ( tbWidth <= 32 ) && ( tbHeight <= 32 )   && ( IntraSubPartitionsSplit[ x0 ][ y0 ] = = ISP_NO_SPLIT ) && ( !cu_sbt_flag ) ) {   if( transform_skip_enabled_flag && tbWidth <= MaxTsSize && tbHeight <= MaxTsSize )    transform_skip_flag[ x0 ][ y0 ] ae(v)   if( (( CuPredMode[ x0 ][ y0 ] != MODE_INTRA && sps_explicit_mts_inter_enabled_flag )    | | ( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA && sps_explicit_mts_intra_enabled_flag ))    && ( tbWidth <= 32 ) && ( tbHeight <= 32 ) && ( !transform_skip_flag[x0 ][ y0 ] ) )    tu_mts_idx[ x0 ][ y0 ] ae(v)  }  if( tu_cbf_luma[ x0 ][ y0 ] )   residual_coding( x0, y0, Log2( tbWidth ), Log2( tbHeight ), 0 )  if( tu_cbf_cb[ x0 ][ y0 ] )   residual_coding( xC, yC, Log2( wC ), Log2( hC ), 1 )  if( tu_cbf_cr[ x0 ][ y0 ] )   residual_coding( xC, yC, Log2( wC ), Log2( hC ), 2 ) } transform_skip_flag[x0][y0] specifies whether a transform is applied to the luma transform block or not. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered transform block relative to the top-left luma sample of the picture. transform_skip_flag[x0][y0] equal to 1 specifies that no transform is applied to the luma transform block. transform_skip_flag[x0][y0] equal to 0 specifies that the decision whether transform is applied to the luma transform block or not depends on other syntax elements. When transform_skip_flag[x0][y0] is not present, it is inferred to be equal to 0. tu_mts_idx[x0][y0] specifies which transform kernels are applied to the residual samples along the horizontal and vertical direction of the associated luma transform block. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered transform block relative to the top-left luma sample of the picture. When tu_mts_idx[x0][y0] is not present, it is inferred to be equal to 0. In the CABAC decoding process, one context is used to decode transform_skip_flag, truncated unary is used to binarize the tu_mts_idx. Each bin of the tu_mts_idx is context coded, and for the first bin, the quad-tree depth (i.e., cqtDepth) is used to select one context; and for the remaining bins, one context is used.

TABLE 9-15 Assignment of ctxinc to syntax elements with context coded bins binIdx Syntax element 0 1 2 3 4 >=5 transform_skip_flag[ ][ ] 0 na na na na na tu_mts_idx[ ][ ] cqtDepth 6 7 8 na na

2.6.2 Implicit MTS

It is noted that ISP, SBT, and MTS enabled but with implicit signalling are all treated as implicit MTS. In the specification, the implicitMtsEnabled is used to define whether implicit MTS is enabled.

8.7.4 Transformation Process for Scaled Transform Coefficients 8.7.4.1 General

The variable implicitMtsEnabled is derived as follows:

-   -   If sps_mts_enabled_flag is equal to 1 and one of the following         conditions is true, implicitMtsEnabled is set equal to 1:         -   IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT         -   cu_sbt_flag is equal to 1 and Max(nTbW, nTbH) is less than             or equal to 32         -   sps_explicit_mts_intra_enabled_flag and             sps_explicit_mts_inter_enabled_flag are both equal to 0 and             CuPredMode[xTbY][yTbY] is equal to MODE_INTRA     -   Otherwise, implicitMtsEnabled is set equal to 0.         The variable trTypeHor specifying the horizontal transform         kernel and the variable trTypeVer specifying the vertical         transform kernel are derived as follows:     -   If cIdx is greater than 0, trTypeHor and trTypeVer are set equal         to 0.     -   Otherwise, if implicitMtsEnabled is equal to 1, the following         applies:         -   If IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT,             trTypeHor and trTypeVer are specified in Table 8-15             depending on intraPredMode.         -   Otherwise, if cu_sbt_flag is equal to 1, trTypeHor and             trTypeVer are specified in Table 8-14 depending on             cu_sbt_horizontal_flag and cu_sbt_pos_flag.         -   Otherwise (sps_explicit_mts_intra_enabled_flag and             sps_explicit_mts_inter_enabled_flag are equal to 0),             trTypeHor and trTypeVer are derived as follows:

trTypeHor=(nTbW>=4 && nTbW<=16 && nTbW<=nTbH)?1:0  (8-1030)

trTypeVer=(nTbH>=4 && nTbH<=16 && nTbH<=nTbW)?1:0  (8-1031)

-   -   Otherwise, trTypeHor and trTypeVer are specified in Table 8-13         depending on tu_mts_idx[xTbY][yTbY].

TABLE 8-13 Specification of trTypeHor and trTypeVer depending on tu_mts_idx[ x ][ y ] tu_mts_idx[ x0 ][ y0 ] 0 1 2 3 4 trTypeHor 0 1 2 1 2 trTypeVer 0 1 1 2 2

TABLE 8-14 Specification of trTypeHor and trTypeVer depending on cu_sbt_horizontal_flag and cu_sbt_pos_flag cu_sbt_horizontal_flag cu_sbt_pos_flag trTypeHor trTypeVer 0 0 2 1 0 1 1 1 1 0 1 2 1 1 1 1

2.7 Reduced Secondary Transform (RST) Proposed in JVET-N0193 2.7.1 Non-Separable Secondary Transform (NSST) in JEM

In JEM, secondary transform is applied between forward primary transform and quantization (at encoder) and between de-quantization and inverse primary transform (at decoder side). As shown in FIG. 11 , 4×4 (or 8×8) secondary transform is performed depending on block size. For example, 4×4 secondary transform is applied for small blocks (i.e., min (width, height)<8) and 8×8 secondary transform is applied for larger blocks (i.e., min (width, height)>4) per 8×8 block.

Application of a non-separable transform is described as follows using input as an example. To apply the non-separable transform, the 4×4 input block X

$X = \begin{bmatrix} X_{00} & X_{01} & X_{02} & X_{03} \\ X_{10} & X_{11} & X_{12} & X_{13} \\ X_{20} & X_{21} & X_{22} & X_{23} \\ X_{30} & X_{31} & X_{32} & X_{33} \end{bmatrix}$

is first represented as a vector

:

=[X₀₀ X₀₁ X₀₂ X₀₃ X₁₀ X₁₁ X₁₂ X₁₃ X₂₀ X₂₁ X₂₂ X₂₃ X₃₀ X₃₁ X₃₂ X₃₃]^(T)

The non-separable transform is calculated as

=T·

, where

indicates the transform coefficient vector, and T is a 16×16 transform matrix. The 16×1 coefficient vector

is subsequently re-organized as 4×4 block using the scanning order for that block (horizontal, vertical or diagonal). The coefficients with a smaller index will be placed with the smaller scanning index in the 4×4 coefficient block. There are a total of 35 transform sets and 3 non-separable transform matrices (kernels) per transform set are used. The mapping from the intra prediction mode to the transform set is pre-defined. For each transform set, the selected non-separable secondary transform (NSST) candidate is further specified by the explicitly signalled secondary transform index. The index is signalled in a bit-stream once per Intra CU after transform coefficients.

2.7.2 RST in JVET-N0193

The RST (also referred to as a low-frequency non-separable transform (LFNST)) was introduced in JVET-K0099 and 4 transform set (instead of 35 transform sets) mapping introduced in JVET-L0133. In this JVET-N0193, 16×64 (further reduced to 16×48) and 16×16 matrices are employed. For notational convenience, the 16×64 (reduced to 16×48) transform is denoted as RST8×8 and the 16×16 transform is denoted as RST4×4. FIG. 12 shows an example of RST.

2.8 Sub-Block Transform (SBT)

For an inter-predicted CU with cu_cbf equal to 1, cu_sbt_flag may be signalled to indicate whether the whole residual block or a sub-part of the residual block is decoded. In the former case, inter MTS information is further parsed to determine the transform type of the CU. In the latter case, a part of the residual block is coded with inferred adaptive transform and the other part of the residual block is zeroed out. The SBT is not applied to the combined inter-intra mode.

In sub-block transform, position-dependent transform is applied on luma transform blocks in SBT-V and SBT-H (chroma TB always using DCT-2). The two positions of SBT-H and SBT-V are associated with different core transforms. More specifically, the horizontal and vertical transforms for each SBT position are specified in FIG. 13 . For example, the horizontal and vertical transforms for SBT-V position 0 are DCT-8 and DST-7, respectively. When one side of the residual transform unit (TU) is greater than 32, the corresponding transform is set as DCT-2. Therefore, the sub-block transform jointly specifies the TU tiling, CBF, and horizontal and vertical transforms of a residual block, which may be considered a syntax shortcut for the cases that the major residual of a block is at one side of the block.

2.8.1 Syntax Elements and Semantics 7.3.7.5 Coding Unit Syntax

Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {  if( slice_type != I | | sps_ibc_enabled_flag ) {   if( treeType != DUAL_TREE_CHROMA )    cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && slice_type != I )    pred_mode_flag ae(v)   if( ( ( slice_type = = I && cu_skip_flag[ x0 ][ y0 ] = =0 ) | |    ( slice_type != I && CuPredMode[ x0 ][ y0 ] != MODE_INTRA ) ) &&    sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) { ...  } else if( treeType != DUAL_TREE_CHROMA ) { /* MODE_INTER or MODE_IBC */ ...  }  if( !pcm_flag[ x0 ][ y0 ] ) {   if( CuPredMode[ x0 ][ y0 ] != MODE_INTRA && merge_flag[ x0 ][ y0 ] = = 0 )    cu_cbf ae(v)   if( cu_cbf ) {    if( CuPredMode[ x0 ][ y0 ] = = MODE_INTER && sps_sbt_enabled_flag &&     !ciip_flag[ x0 ][ y0 ] ) {     if( cbWidth <= MaxSbtSize && cbHeight <= MaxSbtSize ) {      allowSbtVerH = cbWidth >= 8      allowSbtVerQ = cbWidth >= 16      allowSbtHorH = cbHeight >= 8      allowSbtHorQ = cbHeight >= 16      if( allowSbtVerH | | allowSbtHorH | | allowSbtVerQ | | allowSbtHorQ )       cu_sbt_flag ae(v)     }     if( cu_sbt_flag ) {      if( ( allowSbtVerH | | allowSbtHorH ) && ( allowSbtVerQ | | allowSbtHorQ) )       cu_sbt_quad_flag ae(v)      if( ( cu_sbt_quad_flag && allowSbtVerQ && allowSbtHorQ ) | |       ( !cu_sbt_quad_flag && allowSbtVerH && allowSbtHorH ) )       cu_sbt_horizontal_flag ae(v)      cu_sbt_pos_flag ae(v)     }    }    transform_tree( x0, y0, cbWidth, cbHeight, treeType )   }  } }

7.3.7.11 Residual Coding Syntax

Descriptor residual_coding( x0, y0, log2TbWidth, log2TbHeight, cIdx ) {  if( ( tu_mts_idx[ x0 ][ y0 ] > 0 | |    ( cu_sbt_flag && log2TbWidth < 6 && log2TbHeight < 6 ) )     && cIdx = = 0 && log2TbWidth > 4 )   log2TbWidth = 4  else   log2TbWidth = Min(log2TbWidth, 5 )  if( tu_mts_idx[ x0 ][ y0 ] > 0 | |    ( cu_sbt_flag && log2TbWidth < 6 && log2TbHeight < 6 ) )     && cIdx = = 0 && log2TbHeight > 4 )   log2TbHeight = 4  else   log2TbHeight = Min( log2TbHeight, 5 )  if( log2TbWidth > 0 )   last_sig_coeff_x_prefix ae(v)  if( log2TbHeight > 0 )   last_sig_coeff_y_prefix ae(v)  if( last_sig_coeff_x_prefix > 3 )   last_sig_coeff_x_suffix ae(v)  if( last_sig_coeff_y_prefix > 3 )   last_sig_coeff_y_suffix ae(v)  log2SbW = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 )  log2SbH = log2SbW  if ( log2TbWidth < 2 && cIdx = = 0 ) {   log2SbW = log2TbWidth   log2SbH = 4 − log2SbW  } else if ( log2TbHeight < 2 && cIdx = = 0 ) {   log2SbH = log2TbHeight   log2SbW = 4 − log2SbH  }  numSbCoeff = 1 << ( log2SbW + log2SbH )  lastScanPos = numSbCoeff  lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − ( log2SbW + log2SbH ) ) ) − 1 ... } sps_sbt_max_size_64_flag equal to 0 specifies that the maximum CU width and height for allowing subblock transform is 32 luma samples. sps_sbt_max_size_64_flag equal to 1 specifies that the maximum CU width and height for allowing subblock transform is 64 luma samples.

MaxSbtSize=sps_sbt_max_size_64_flag?64:32  (7-33)

2.9 Quantized Residual Domain Block Differential Pulse-Code Modulation (BDPCM) Coding (QR-BDPCM)

In JVET-N0413, quantized residual domain BDPCM (denoted as QR-BDPCM hereinafter) is proposed. The intra prediction is done on the entire block by sample copying in the prediction direction (horizontal or vertical prediction) similar to intra prediction. The residual is quantized and the delta between the quantized residual and its predictor (horizontal or vertical) quantized value is coded.

For a block of size M (rows)×N (cols), let r_(i,j), 0≤i≤M−1, 0≤j≤N−1, be the prediction residual after performing intra prediction horizontally (copying left neighbor pixel value across the predicted block line by line) or vertically (copying top neighbor line to each line in the predicted block) using unfiltered samples from above or left block boundary samples. Let Q(r,j), 0≤i≤M−1, 0≤j≤N−1 denote the quantized version of the residual r_(i,j), where residual is the difference between original block and the predicted block values. Then the block differential pulse-code modulation (DPCM) is applied to the quantized residual samples, resulting in modified M×N array {tilde over (R)} with elements {tilde over (r)}_(i,j). When vertical BDPCM is signalled:

${\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix} {{Q\left( r_{i,j} \right)},} & {{i = 0},{0 \leq j \leq \left( {N - 1} \right)}} \\ {{{Q\left( r_{i,j} \right)} - {Q\left( r_{{({i - 1})},j} \right)}},} & {{1 \leq i \leq \left( {M - 1} \right)},{0 \leq j \leq \left( {N - 1} \right)}} \end{matrix} \right.$

For horizontal prediction, similar rules apply, and the residual quantized samples are obtained by:

${\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix} {{Q\left( r_{i,j} \right)},} & {{0 \leq i \leq \left( {M - 1} \right)},{j = 0}} \\ {{{Q\left( r_{i,j} \right)} - {Q\left( r_{i,{({j - 1})}} \right)}},} & {{0 \leq i \leq \left( {M - 1} \right)},{1 \leq j \leq \left( {N - 1} \right)}} \end{matrix} \right.$

The residual quantized samples {tilde over (r)}_(i,j) are sent to the decoder.

On the decoder side, the above calculations are reversed to produce Q(r_(i,j)), 0≤i≤M−1, 0≤j≤N−1. For vertical prediction case,

Q(r _(i,j))=Σ_(k=0) ^(i) {tilde over (r)} _(k,j), 0≤i≤(M−1), 0≤j≤(N−1)

For horizontal case,

Q(r _(i,j))=Σ_(k=0) ^(j) {tilde over (r)} _(i,k), 0≤i≤(M−1), 0≤j≤(N−1)

The inverse quantized residuals, Q⁻¹(Q(r,j)), are added to the intra block prediction values to produce the reconstructed sample values.

Transform skip is always used in the QR-BDPCM.

2.9.1 Coefficients Coding of TS-Coded Blocks and QR-BDPCM Coded Blocks

QR-BDPCM follows the context modeling method for TS-coded blocks.

A modified transform coefficient level coding for the TS residual. Relative to the regular residual coding case, the residual coding for TS includes the following changes:

-   -   (1) no signalling of the last x/y position;     -   (2) coded_sub_block_flag coded for every subblock except for the         last subblock when all previous flags are equal to 0;     -   (3) sig_coeff_flag context modelling with reduced template;     -   (4) a single context model for abs_level_gt1_flag and         par_level_flag;     -   (5) context modeling for the sign flag, additional greater than         5, 7, 9 flags;     -   (6) modified Rice parameter derivation for the remainder         binarization; and     -   (7) a limit for the number of context coded bins per sample, 2         bins per sample within one block.

2.9.2 Syntax and Semantics 7.3.6.5 Coding Unit Syntax

Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {  if( tile_group_type != I | | sps_ibc_enabled_flag ) {   if( treeType != DUAL_TREE_CHROMA )    cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && tile_group_type != I )    pred_mode_flag ae(v)   if( ( ( tile_group_type = = I && cu_skip_flag[ x0 ][ y0 ] = =0 ) | |    ( tile_group_type != I && CuPredMode[ x0 ][ y0 ] != MODE_INTRA ) ) &&    sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) {   if( pred_mode_flag = = MODE_INTRA&& ( cIdx == 0 ) &&    ( cbWidth <=32 ) && ( CbHeight <= 32 )) {    bdpcm_flag[ x0 ][ y0 ] ae(v)    if( bdpcm_flag[ x0 ][ y0 ] ) {     bdpcm_dir_flag[ x0 ][ y0 ] ae(v)    }    else {   if( sps_pcm_enabled_flag &&    cbWidth >= MinIpcmCbSizeY && cbWidth <= MaxIpcmCbSizeY &&    cbHeight >= MinIpcmCbSizeY && cbHeight <= MaxIpcmCbSizeY )    pcm_flag[ x0 ][ y0 ] ae(v)   if( pcm_flag[ x0 ][ y0 ] ) {    while( !byte_aligned( ) )     pcm_alignment_zero_bit f(1)    pcm_sample( cbWidth, cbHeight, treeType)   } else {    if( treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_LUMA ) {     if( ( y0 % CtbSizeY ) > 0 )      intra_luma_ref_idx[ x0 ][ y0 ] ae(v)     if (intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&      ( cbWidth <= MaxTbSizeY | | cbHeight <= MaxTbSizeY ) &&      ( cbWidth * cbHeight > MinTbSizeY * MinTbSizeY ))      intra_subpartitions_mode_flag[ x0 ][ y0 ] ae(v)     if( intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 1 &&      cbWidth <= MaxTbSizeY && cbHeight <= MaxTbSizeY )      intra_subpartitions_split_flag[ x0 ][ y0 ] ae(v)     if( intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&      intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 0 )      intra_luma_mpm_flag[ x0 ][ y0 ] ae(v)     if( intra_luma_mpm_flag[ x0 ][ y0 ] )      intra_luma_mpm_idx[ x0 ][ y0 ] ae(v)     else      intra_luma_mpm_remainder[ x0 ][ y0 ] ae(v)    }    }    if( treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_CHROMA )     intra_chroma_pred_mode[ x0 ][ y0 ] ae(v)   }  } else if( treeType != DUAL_TREE_CHROMA) { /* MODE_INTER or MODE_IBC */ ... } bdpcm_flag[x0][y0] equal to 1 specifies that a bdpcm_dir_flag is present in the coding unit including the luma coding block at the location (x0, y0) bdpcm_dir_flag[x0][y0] equal to 0 specifies that the prediction direction to be used in a bdpcm block is horizontal, otherwise it is vertical.

7.3.6.10 Transform Unit Syntax

Descriptor transform_unit( x0, y0, tbWidth, tbHeight, treeType, subTuIndex ) { ...  if( tu_cbf_luma[ x0 ][ y0 ] && treeType != DUAL_TREE_CHROMA   && ( tbWidth <= 32 ) && ( tbHeight <= 32 )   && ( IntraSubPartitionsSplit[ x0 ][ y0 ] = = ISP_NO_SPLIT ) && ( !cu_sbt_flag ) ) {   if( transform_skip_enabled_flag && tbWidth <= MaxTsSize && tbHeight <= MaxTsSize )    transform_skip_flag[ x0 ][ y0 ] ae(v)   if( (( CuPredMode[ x0 ][ y0 ] != MODE_INTRA && sps_explicit_mts_inter_enabled_flag )    | | ( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA && sps_explicit_mts_intra_enabled_flag ))    && ( tbWidth <= 32 ) && ( tbHeight <= 32 ) && ( !transform_skip_flag[ x0 ][ y0 ] ) )    tu_mts_idx[ x0 ][ y0 ] ae(v)  }  if( tu_cbf_luma[ x0 ][ y0 ] ) {   if( !transform_skip_flag[ x0 ][ y0 ] )    residual_coding( x0, y0, Log2( tbWidth ), Log2( tbHeight ), 0 )   else    residual_coding_ts( x0, y0, Log2( tbWidth ), Log2( tbHeight ), 0 )  }  if( tu_cbf_cb[ x0 ][ y0 ] )   residual_coding( xC,yC,Log2( wC ),Log2( hC ), 1 )  if( tu_cbf_cr[ x0 ][ y0 ] )   residual_coding( xC,yC,Log2( wC ),Log2( hC ), 2 ) } Descriptor residual_ts_coding( x0, y0, log2TbWidth, log2TbHeight, cIdx ) {  log2SbSize = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 )  numSbCoeff = 1 << ( log2SbSize << 1 )  lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − 2 * log2SbSize ) ) − 1 /* Loop over subblocks from top-left(DC) subblock to the last one */  inferSbCbf = 1  MaxCcbs = 2 * ( 1 << log2TbWidth ) * ( 1 << log2TbHeight )  for( i =0; i <= lastSubBlock; i++ ) {   xS = DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ][ i ][ 0 ]   yS = DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ][ i ][ 1 ]   if( ( i != lastSubBlock | | !inferSbCbf)    coded_sub_block_flag[ xS ][ yS ] ae(v)    MaxCcbs− −   if( coded_sub_block_flag[ xS ][ yS ] && i < lastSubBlock )    inferSbCbf = 0   }  /* First scan pass */   inferSbSigCoeffFlag = 1   for( n = ( i = = 0; n <= numSbCoeff − 1; n++ ) {    xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] &&     ( n == numSbCoeff− 1 | | !inferSbSigCoefFFlag ) ) {     sig_coeff_flag[ xC ][ y C ] ae(v)     MaxCcbs− −     if( sig_coeff_flag[ xC ][ yC ] )      inferSbSigCoeffFlag = 0    }    if( sig_coeff_flag[ xC ][ yC ] ) {     coeff_sign_flag[ n ] ae(v)     abs_level_gtx_flag[ n ][ 0 ] ae(v)     MaxCcbs = MaxCcbs − 2     if( abs_level_gtx_flag[ n ][ 0 ] ) {      par_level_flag[ n ] ae(v)      MaxCcbs− −     }    }    AbsLevelPassX[ xC ][ yC ] =      sig_coeff_flag[ xC ][ yC ] + par_level_flag[ n ] + abs_level_gtx_flag[ n ][ 0 ]   }  /* Greater than X scan passes (numGtXFlags=5) */   for( i = 1; i <= 5 − 1 && abs_level_gtx_flag[ n ][ i − 1 ] ; i++ ) {    for( n = 0; n <= numSbCoeff − 1; n++ ) {     xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]     yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]     abs_level_gtx_flag[ n ][ i ] ae(v)     MaxCcbs− −  AbsLevelPassX[ xC ][ yC ] + = 2 * abs_level_gtx_flag[ n ][ i ]    }   }  /* remainder scanpass */   for( n = 0; n <= numSbCoeff − 1; n++ ) {    xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]    if( abs_level_gtx_flag[ n ][ numGtXFlags − 1 ] )     abs_remainder[ n ] ae(v)    TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 * coeff_sign_flag[ n ] ) *  ( AbsLevelPassX[ xC ][ yC ] + abs_remainder[ n ] )   }  } } The number of context coded bins is restricted to be no larger than 2 bins per sample for each CG.

TABLE 9-15 Assignment of ctxinc to syntax elements with context coded bins binIdx Syntax element 0 1 2 3 4 >= 5 last_sig_coeff_x_prefix 0..23 (clause 9.5.4.2.4) last_sig_coeff_y_prefix 0..23 (clause 9.5.4.2.4) last_sig_coeff_x_suffix bypass bypass bypass bypass bypass bypass last_sig_coeff_y_suffix bypass bypass bypass bypass bypass bypass coded_sub_block_flag[ ][ ] ( MaxCcbs > 0) ? (0..7 na na na na na (clause 9.5.4.2.6)) : bypass sig_coeff_flag[ ][ ] (MaxCcbs > 0) ? (0..93 na na na na na (clause 9.5.4.2.8)) : bypass par_level_flag[ ] (MaxCcbs > 0) ? (0..33 na na na na na (clause 9.5.4.2.9)) : bypass abs_level_gtx_flag[ ] [ i ] 0..70 na na na na na (clause 9.5.4.2.9) abs remainder[ ] bypass bypass bypass bypass bypass bypass dec_abs_level[ ] bypass bypass bypass bypass bypass bypass coeff_sign_flag[ ] bypass na na na na na transform skip_flag[ x0 ][ y0 ] = = 0 coeff_sign_flag[ ] 0 na na na na na transform skip_flag[ x0 ][ y0 ] = = 1

2.10 In-Loop Reshaping (ILR) in JVET-M0427

The basic idea of ILR is to convert the original (in the first domain) signal (prediction/reconstruction signal) to a second domain (reshaped domain).

The in-loop luma reshaper is implemented as a pair of look-up tables (LUTs), but only one of the two LUTs need to be signalled as the other one can be computed from the signalled LUT. Each LUT is a one-dimensional, 10-bit, 1024-entry mapping table (1D-LUT). One LUT is a forward LUT, FWALUT, that maps input luma code values Y₁ to altered values Y_(r):Y_(r)=FwdLUT[Y_(i)]. The other LUT is an inverse LUT, InvLUT, that maps altered code values Y_(r) to Ŷ_(i): Ŷ_(i)=InvLUT[Y_(r)]. (Ŷ_(i) represents the reconstruction values of Y_(i)).

ILR is also known as luma mapping with chroma scaling (LMCS) in VVC.

2.10.1 Piecewise Linear (PWL) Model

Conceptually, PWL is implemented in the following way:

Let x1, x2 be two input pivot points, and y1, y2 be their corresponding output pivot points for one piece. The output value y for any input value x between x1 and x2 can be interpolated by the following equation:

y=((y2−y1)/(x2−x1))*(x−x1)+y1

In fixed point implementation, the equation can be rewritten as:

y=((m*x+2FP_PREC−1)>>FP_PREC)+c

Herein, m is scalar, c is an offset, and FP_PREC is a constant value to specify the precision.

Note that in CE-12 software, the PWL model is used to precompute the 1024-entry FwdLUT and InvLUT mapping tables; but the PWL model also allows implementations to calculate identical mapping values on-the-fly without pre-computing the LUTs.

2.10.2 Luma Reshaping

Test 2 of the in-loop luma reshaping (i.e., CE12-2 in the proposal) provides a lower complexity pipeline that also eliminates decoding latency for block-wise intra prediction in inter slice reconstruction. Intra prediction is performed in reshaped domain for both inter and intra slices.

Intra prediction is always performed in reshaped domain regardless of slice type. With such arrangement, intra prediction can start immediately after previous transform unit (TU) reconstruction is done. Such arrangement can also provide a unified process for intra mode instead of being slice dependent. FIG. 14 shows the block diagram of the CE12-2 decoding process based on mode.

CE12-2 also tests 16-piece PWL models for luma and chroma residue scaling instead of the 32-piece PWL models of CE12-1.

Inter slice reconstruction with in-loop luma reshaper in CE12-2 (lighter shaded blocks indicate signal in reshaped domain: luma residue; intra luma predicted; and intra luma reconstructed).

2.10.3 Luma-Dependent Chroma Residue Scaling

Luma-dependent chroma residue scaling is a multiplicative process implemented with fixed-point integer operation. Chroma residue scaling compensates for luma signal interaction with the chroma signal. Chroma residue scaling is applied at the TU level. More specifically, the average value of the corresponding luma prediction block is utilized.

The average is used to identify an index in a PWL model. The index identifies a scaling factor cScaleInv. The chroma residual is multiplied by that number.

It is noted that the chroma scaling factor is calculated from forward-mapped predicted luma values rather than reconstructed luma values.

2.10.4 Usage of ILR

At the encoder side, each picture (or tile group) is first converted to the reshaped domain. And all the coding process is performed in the reshaped domain. For intra prediction, the neighboring block is in the reshaped domain; for inter prediction, the reference blocks (generated from the original domain from decoded picture buffer) are first converted to the reshaped domain. Then the residuals are generated and coded to the bitstream.

After the whole picture (or tile group) finishes encoding/decoding, samples in the reshaped domain are converted to the original domain, then deblocking filter and other filters are applied.

Forward reshaping to the prediction signal is disabled for the following cases:

-   -   Current block is intra-coded     -   Current block is coded as current picture referencing (CPR),         which may also be referred to as intra block copy (IBC)     -   Current block is coded as combined inter-intra mode (CIIP) and         the forward reshaping is disabled for the intra prediction block

3 Drawbacks of Existing Implementations

The current design has the following problems:

(1) LMCS may be still applied to a block coded with transform and quantization bypass mode (i.e., cu_transquant_bypass_flag equal to 1). However, the mapping from original domain to reshaped domain, or vice versa, are lossy. Enabling both LMCS and cu_transquant_bypass_flag is not desirable.

(2) How to signal several new transform related coding tools (such as MTS index or RST index or SBT), coding tools without transform (such as QR-BDPCM) and cu_transquant_bypass_flag has not been studied.

(3) cu_transquant_bypass_flag in HEVC was signalled once and applied to all three-color components. How to handle dual tree needs to be studied.

4 Example Methods for Lossless Coding for Visual Media Coding

Embodiments of the present disclosure overcome the drawbacks of existing implementations, thereby providing video coding with higher coding efficiencies. The methods for the lossless coding for visual media coding, based on the disclosed embodiments, may enhance both existing and future video coding standards, is elucidated in the following examples described for various embodiments. The examples of the disclosed embodiments provided below explain general concepts, and are not meant to be interpreted as limiting. In an example, unless explicitly indicated to the contrary, the various features described in these examples may be combined.

Denote one block size by W*H, wherein W is the block width and H is the block height. The maximum transform block size denoted by MaxTbW*MaxTbH, wherein MaxTbW and MaxTbH are the maximum transform block width and height, respectively. The minimum transform block size denoted by MinTbW*MinTbH, wherein MinTbW and MinTbH are the minimum transform block width and height, respectively.

TransQuantBypass mode is defined such that transform and quantization process are skipped, such as cu_transquant_bypass_flag being set to 1.

Usage of TransQuantBypass Mode for Multiple Color Components

-   -   1. Indications of TransQuantBypass mode (e.g.,         cu_transquant_bypass_flag) may be signalled separately for         different color components.         -   a. In one example, when dual tree is enabled,             cu_transquant_bypass_flag for luma and chroma components or             for each color component may be coded separately.         -   b. In one example, usage of this mode may be context coded.             -   i. In one example, the selection of context may depend                 on the color component.         -   c. In one example, predictive coding of this flag may be             applied.         -   d. In one example, whether to signal multiple indications or             just one for all color components may depend on the coding             structure (e.g., single tree or dual tree).         -   e. In one example, whether to signal multiple indications or             just one for all color components may depend on color             formats and/or color component coding methods (e.g.,             separate plane coding is enabled or not) and/or coding mode.             -   i. In one example, when joint chroma residual coding is                 enabled for chroma blocks, the two chroma blocks may                 share the same enabling flag of TransQuantBypass.     -   2. Indications of TransQuantBypass mode (e.g.,         cu_transquant_bypass_flag) for chroma blocks may be derived from         the corresponding luma region.         -   a. In one example, if a chroma block corresponds to a luma             region which covers one or multiple blocks such as coding             units (CU) or prediction unit (PU) or transform unit (TU),             and at least one luma block is coded with TransQuantBypass             mode, then the chroma block should be coded with             TransQuantBypass mode.             -   i. Alternatively, if a chroma block corresponds to a                 luma region which covers one or multiple blocks and all                 these luma blocks is coded with TransQuantBypass mode,                 then the chroma block should be coded with                 TransQuantBypass mode.             -   ii. Alternatively, a chroma block may be divided into                 sub-blocks. If a sub-block corresponds to a luma region                 which covers one or multiple blocks and at all these                 luma blocks is coded with TransQuantBypass mode, then                 the chroma sub-block should be coded with                 TransQuantBypass mode.     -   3. TransQuantBypass mode may be enabled for a block larger than         a virtual pipeline data unit (VPDU).         -   a. A block is defined to be larger than a VPDU if its width             or height is larger than the width or height of the VPDU.             -   i. Alternatively, a block is defined to be larger than a                 VPDU if both its width and height are larger than the                 width and height of the VPDU, respectively.         -   b. In one example, indications of TransQuantBypass mode             (e.g., cu_transquant_bypass_flag) cu_transquant_bypass_flag             may be signalled for a block larger than a VPDU.         -   c. In one example, for CTUs larger than a VPDU, it may be             split via quad-tree until reaching multiple VPDUs or it may             not be split. When not split, the cu_transquant_bypass_flag             may be inferred to be 1 without being signalled.             -   i. Alternatively, intra prediction mode may be allowed                 for those large blocks.     -   4. Transform skip mode and/or other coding methods which do not         apply transform may be enabled for a block larger than a VPDU.         -   a. A block is defined to be larger than a VPDU if its width             or height is larger than the width or height of the VPDU.             -   i. Alternatively, a block is defined to be larger than a                 VPDU if both its width and height are larger than the                 width and height of the VPDU, respectively.         -   b. In one example, indications of transform skip mode may be             signalled for a block larger than a VPDU.         -   c. In one example, for CTUs larger than a VPDU, it may be             split via quad-tree until reaching multiple VPDUs or it may             not be split. When not split, the transform skip flag may be             inferred to be 1 without being signalled.             -   i. Alternatively, intra prediction mode may be allowed                 for those large blocks.         -   d. Other coding methods which do not apply transform may             include transform skip mode, DPCM, QR-BDPCM, etc.

Block Dimension Settings of TransQuantBypass Mode

-   -   5. The allowed block dimensions for TransQuantBypass mode may be         the same as that TS may be enabled.         -   a. TransQuantBypass mode may be applicable to same block             dimensions that QR-BDPCM may be enabled.         -   b. Maximum and/or minimum block dimensions for blocks with             TransQuantBypass mode may be signalled in             sequence/view/picture/slice/tile group/tile/CTUs/video             units-level.             -   i. In one example, indications of Maximum and/or minimum                 block dimensions for blocks with                 cu_transquant_bypass_flag may be signalled in sequence                 parameter set (SPS)/video parameter set (VPS)/picture                 parameter set (PPS)/slice header/tile group header/tile,                 etc.     -   6. It is proposed to align the allowed block dimensions for all         kinds of coding modes for which transform is disabled, such as         TS, TransQuantBypass mode, QR-BDPCM, BDPCM, etc.         -   a. Alternatively, a single indication of the allowed maximum             and/or minimum size for those cases may be signalled to             control usage of all of those modes.

Interaction Between TransQuantBypass Mode and Other Coding Tools

-   -   7. For TransQuantBypass-coded block, luma reshaping and/or         chroma scaling may be disabled.         -   a. When TransQuantBypass is applied to a block, the residual             is coded in the original domain instead of the reshaped             domain regardless the enabling/disabling flag of the LMCS.             For example, the enabling/disabling flag of the LMCS may be             signalled in slice/sequence level.         -   b. In one example, for an intra and TransQuantBypass-coded             block, the prediction signal/reference samples used in intra             prediction may be first mapped from reshaped domain to             original domain.         -   c. In one example, for an IBC and TransQuantBypass-coded             block, the prediction signal/reference samples used in IBC             prediction may be first mapped from reshaped domain to             original domain.         -   d. In one example, for a CIIP and TransQuantBypass-coded             block, the following may apply:             -   i. The prediction signal of intra prediction/reference                 samples used in intra prediction may be first mapped                 from reshaped domain to original domain.             -   ii. The mapping of prediction signal of inter prediction                 from original domain to the reshaped domain is skipped.         -   e. In one example, for the palette mode, the palette table             may be generated in the original domain instead of reshaped             domain.         -   f. Alternatively, two buffers may be allocated, one of which             is to store the summation of prediction signal and residual             signal (a.k.a., the reconstructed signal); and the other is             to store the reshaped summation, that is, the summation of             prediction signal and residual signal need to be first             mapped from original domain to reshaped domain and may be             further utilized for coding succeeding blocks.             -   i. Alternatively, only the reconstructed signal in the                 original domain is stored. The reconstructed signal in                 the reshaped domain may be converted from the                 reconstructed signal in the original domain when                 required by succeeding blocks.         -   g. The above methods may be applicable to other coding             methods which rely on reference samples within current             tile/slice/tile group/picture.             -   i. In one example, inverse reshaping process (i.e.,                 conversion from the reshaped domain to the original                 domain) may be applied on the prediction signal                 generated from reference samples within current                 tile/slice/tile group/picture.             -   ii. Alternatively, furthermore, the forward reshaping                 process (i.e., conversion from the original domain to                 the reshaped domain) is not allowed to be applied on the                 prediction signal generated from reference samples in a                 different picture, such as in a reference picture.         -   h. In one example, luma reshaping and/or chroma scaling may             be disabled for blocks coded with methods which do not apply             transform (e.g., TS mode).             -   i. Alternatively, furthermore, the above claims (e.g.,                 bullets 7 a-g) may be applied by replacing the                 TransQuantBypass mode with a different coding mode                 (e.g., TS).     -   8. The indication of TransQuantBypass mode may be signalled         before signalling one or multiple transform matrices related         coding tools.         -   a. In one example, transform matrices related coding tools             may be one or multiple of the following tools (related             syntax elements are included in parentheses):             -   i. Transform skip mode (e.g., transform_skip_flag)             -   ii. Explicit MTS (e.g., tu_mts_idx)             -   iii. RST (e.g., st_idx)             -   iv. SBT (e.g., cu_sbt_flag, cu_sbt_quad_flag,                 cu_sbt_pos_flag)             -   v. QR-BDPCM (e.g., bdpcm_flag, bdpcm_dir_flag)         -   b. How to code the residual may be dependent on the usage of             TransQuantBypass mode.             -   i. In one example, whether to code residual_coding or                 residual_coding_ts may depend on the usage of                 TransQuantBypass mode.             -   ii. In one example, when TransQuantBypass is disabled                 and transform_skip_flag is disabled, the residual coding                 method which is designed for blocks with transform                 applied to (e.g., residual_coding) may be utilized for                 residual coding.             -   iii. In one example, when TransQuantBypass is enabled or                 transform_skip_flag is enabled, the residual coding                 method which is designed for blocks without transform                 applied (e.g., residual_coding_ts) may be utilized for                 residual coding.         -   c. Alternatively, side information of other kinds of             transform matrices related coding tools may be signalled             under the condition of usage of TransQuantBypass mode.             -   i. When TransQuantBypass mode is applied, side                 information of usage of Transform skip mode, QR-BDPCM,                 BDPCM may be further signalled.             -   ii. When TransQuantBypass mode is applied, side                 information of usage of SBT, RST, MTS may not be                 signalled.     -   9. The indication of TransQuantBypass mode may be signalled         after signalling one or multiple transform matrices related         coding tools.         -   a. Alternatively, indications of TransQuantBypass mode may             be coded when certain coding tool is applied, such as the             Transform skip mode, QR-BDPCM, BDPCM.         -   b. Alternatively, indications of TransQuantBypass mode may             not be coded when certain coding tool is applied, such as             the SBT, RST, MTS.     -   10. The indication of TransQuantBypass mode may be conditionally         signalled after signalling indications of quantization         parameters.         -   a. Alternatively, indications of quantization parameters may             be conditionally signalled after signalling the indication             of TransQuantBypass mode.         -   b. In one example, when TransQuantBypass is applied to one             block, signalling of the quantization parameter and/or delta             of quantization parameters (e.g., cu_qp_delta_abs,             cu_qp_delta_sign_flag) may be skipped.             -   i. For example, cu_qp_delta_abs may be inferred to be 0.         -   c. Alternatively, when delta of quantization parameters             (e.g., cu_qp_delta_abs, cu_qp_delta_sign_flag) is unequal to             0, signalling of TransQuantBypass mode may be skipped, and             TransQuantBypass is inferred to be disabled.             -   i. In one example, the signalling of TransQuantBypass                 may depend on indications of quantization parameters                 only for a specific color component, such as the luma                 component.     -   11. When TransQuantBypass mode is enabled for one block, ALF or         non-linear ALF is disabled for samples in that block.     -   12. When TransQuantBypass mode is enabled for one block,         bilateral filter or/and diffusion filter and/or other kinds of         post-reconstruction filters that may modify the reconstruction         block may be disabled for samples in that block.     -   13. When TransQuantBypass mode is enabled for one block, PDPC         may be disabled.     -   14. The transform selection method in implicit MTS is not         applicable if a block is coded with the TransQuantBypass mode.     -   15. The scaling approach for chroma samples in LMCS is not         applied if a block is coded with the TransQuantBypass mode.     -   16. LMCS may be disabled for CU/CTU/slice/tile/tile         group/picture/sequence wherein TransQuantBypass is allowed.         -   a. In one example, when a SPS/VPS/PPS/slice-level flag             indicates that transform and quantization bypass mode may be             applied to one block within the sequence/view/picture/slice,             LMCS may be disabled.         -   b. Alternatively, the signalling of LMCS related syntax             elements may be skipped.         -   c. In sequence/picture/slice/tile group/tile/brick-level,             TransQuantBypass mode may be disabled when LMCS is enabled.             -   i. For example, the signalling of enabling/disabling                 TransQuantBypass may depend on the usage of LMCS.                 -   1) In one example, the indication of                     TransQuantBypass is not signalled if LMCS is                     applied. E.g., TransQuantBypass is inferred to be                     not used.                 -   2) Alternatively, the signalling of usage of LMCS                     may depend on the enabling/disabling of                     TransQuantBypass.             -   d. In one example, a conformance bitstream shall satisfy                 that TransQuantBypass and LMCS shall not be enabled for                 the same slice/tile/brick/tile group/picture.     -   17. Side information of QR-BDPCM may be signalled after the         signalling of TS mode (e.g., transform_skip_flag).         -   a. In one example, QR-BDPCM is treated as a special case of             TS mode.             -   i. Alternatively, when QR-BCPCM is allowed for one                 block, the TS mode shall be enabled too, that is, the                 signalled/derived transform_skip_flag shall be equal to                 1.             -   ii. Alternatively, when the signalled/derived                 transform_skip_flag shall be equal to 1, the side                 information of QR-BDPCM may be further signalled.             -   iii. Alternatively, when the signalled/derived                 transform_skip_flag shall be equal to 0, the side                 information of QR-BDPCM may not be signalled.         -   b. In one example, QR-BDPCM is treated as a different mode             from the TS mode.             -   i. Alternatively, when the signalled/derived                 transform_skip_flag is equal to 0, the side information                 of QR-BDPCM may be further signalled.             -   ii. Alternatively, when the signalled/derived                 transform_skip_flag is equal to 1, the side information                 of QR-BDPCM may not be further signalled.     -   18. TransQuantBypass mode and/or TS mode and/or other coding         methods that transform are not applied (e.g., palette mode) may         be enabled in a sub-block level instead of whole block (e.g.,         CU/PU).         -   a. In one example, for the dual-tree case, a chroma block             may be split to multiple sub-blocks, each block may             determine the usage of TransQuantBypass mode and/or TS mode             and/or other coding methods that transform are not applied             according to the corresponding luma block's coded             information.     -   19. Whether to apply the inverse reshaping process (i.e.,         conversion from the reshaped domain to the original domain) to         the reconstructed blocks before loop filtering processes may be         changed from block to block.         -   a. In one example, the inverse reshaping process may not be             applied to blocks coded with TransQuantBypass mode but             applied to other blocks coded with non-TransQuantBypass             mode.

The examples described above may be incorporated in the context of the methods described below, e.g., methods 1500 to 1560 and 2100 to 2500, which may be implemented at a video decoder or a video encoder.

FIG. 15A shows a flowchart of an exemplary method 1500 for video processing. The method 1500 includes, at step 1502, configuring, for a current video block comprising a plurality of color components, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is signalled separately in the bitstream representation for at least two color components of the plurality of color components.

The method 1500 includes, at step 1504, performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block. In some embodiments, the current video block comprises a luma component and a plurality of chroma components, and wherein the indication for at least one of the plurality of chroma components is based on the indication for the luma component.

In some embodiments, the indication of skipping the transform and quantization process is denoted as cu_transquant_bypass_flag. In an example, a dual tree partitioning process is enabled for the current video block, and wherein the cu_transquant_bypass_flag is coded separately for a luma component and at least one chroma component of the current video block. In another example, a usage of skipping the transform and quantization process denoted by the cu_transquant_bypass_flag is coded based on a context. In yet another example, the context is selected based on at least one of the plurality of color components.

In some embodiments, signalling the indication separately for the at least two color components is based on at least one of a color format, a color component coding method or a coding mode of the current video block.

FIG. 15B shows a flowchart of another exemplary method 1510 for video processing. The method 1510 includes, at step 1512, making a decision, based on a characteristic of a current video block, regarding an enablement of a mode that skips an application of a transform and quantization process on the current video block.

The method 1510 includes, at step 1514, performing, based on the decision, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments, the characteristic is a size of the current video block, wherein the mode is enabled, and wherein the size of the current video block is larger than a size of a virtual pipelining data unit (VPDU). In an example, a height or a width of the current video block is greater than a height or a width of the VPDU, respectively.

In some embodiments, a coding mode that does not apply a transform is enabled for the current video block. In an example, the coding mode is a transform skip mode, a differential pulse-code modulation (DPCM) mode or a quantized residual DPCM mode.

FIG. 15C shows a flowchart of an exemplary method 1520 for video processing. The method 1520 includes, at step 1522, making a decision, based on at least one dimension of a current video block, regarding an enablement of a first mode that skips an application of a transform and quantization process on the current video block and a second mode that does not apply a transform to the current video block.

The method 1520 includes, at step 1524, performing, based on the decision, a conversion between the current video block and a bitstream representation of the current video block. In some embodiments, the second mode is a transform skip (TS) mode. In other embodiments, the second mode is a quantized residual block differential pulse-code modulation (QR-BDPCM) mode.

In some embodiments, a maximum value or a minimum value of the at least one dimension of the current video block is signalled in a sequence parameter set (SPS), a video parameter set (VPS), a picture parameter set (PPS), a slice header, a tile group header or a tile header.

In some embodiments, an allowed value of the at least one dimension is identical for the first mode and the second mode. In an example, the second mode is one of a transform skip mode, a block differential pulse-code modulation (BDPCM) mode or a quantized residual BDPCM mode.

FIG. 15D shows a flowchart of an exemplary method 1530 for video processing. The method 1530 includes, at step 1532, determining that a current video block is coded using a first mode and a second mode that skips an application of a transform and quantization process on the current video block.

The method 1530 includes, at step 1534, performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block. In some embodiments, the current video block comprises a luma component and a chroma component, and wherein at least one of a reshaping of the luma component or a scaling of the chroma component is disabled.

In some embodiments, the first mode is an intra prediction mode. In other embodiments, the first mode is an intra block copy (IBC) mode. In yet other embodiments, the first mode is a combined inter-intra prediction (CIIP) mode. In an example, reference samples used in the first mode are mapped from a reshaped domain to an original domain.

In some embodiments, the current video block comprises a luma component and a chroma component, wherein the first mode does not apply a transform to the current video block, and wherein an application of a luma mapping with chroma scaling (LMCS) process is disabled for the current video block.

FIG. 15E shows a flowchart of an exemplary method 1540 for video processing. The method 1540 includes, at step 1542, configuring, for a current video block, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is signalled in the bitstream representation before signalling syntax elements related to one or more multiple transform related coding tools.

The method 1540 includes, at step 1544, performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block. In some embodiments, the one or more multiple transform related coding tools include at least one of a transform skip mode, an explicit multiple transform set (MTS) scheme, a reduced secondary transform (RST) mode, a sub-block transform (SBT) mode, or a quantized residual block differential pulse-code modulation (QR-BDPCM) mode.

FIG. 15F shows a flowchart of an exemplary method 1550 for video processing. The method 1550 includes, at step 1552, determining that a current video block is coded using a mode that skips an application of a transform and quantization process on the current video block.

The method 1550 includes, at step 1554, disabling, based on the determining and as part of performing a conversion between the current video block and a bitstream representation of the current video block, a filtering method.

In some embodiments, the filtering method comprises an adaptive loop filtering (ALF) method or a nonlinear ALF method.

In some embodiments, the filtering method uses at least one of a bilateral filter, a diffusion filter or a post-reconstruction filter that modifies a reconstructed version of the current video block.

In some embodiments, the filtering method comprises a position dependent intra prediction combination (PDPC) method.

In some embodiments, the filtering method comprises a loop filtering method, and the method 1550 further includes the step of making a decision, prior to an application of the filtering method, regarding a selective application of an inverse reshaping process to a reconstructed version of the current video block.

FIG. 15G shows a flowchart of an exemplary method 1560 for video processing. The method 1560 includes, at step 1562, determining that a current video block is coded using a mode that skips an application of a transform and quantization process on the current video block.

The method 1560 includes, at step 1564, disabling, based on the determining and as part of performing a conversion between the current video block and a bitstream representation of the current video block, an in-loop reshaping (ILR) process for (i) a current picture comprising the current video block or (ii) a portion of the current picture.

In some embodiments, the portion of the current picture is a coding unit (CU), a coding tree unit (CTU), a slice, a tile or a tile group.

In some embodiments, an indication of the disabling is signalled in a sequence parameter set (SPS), a video parameter set (VPS), a picture parameter set (PPS) or a slice header.

In some embodiments, the bitstream representation of the current video block excludes signalling of syntax elements related to the ILR process.

Yet another method for video processing includes configuring, for a current video block, a bitstream representation of the current video block, wherein an indication of skipping a transform and quantization process is selectively signalled in the bitstream representation after signalling one or more indications of quantization parameters; and performing, based on the configuring, a conversion between the current video block and the bitstream representation of the current video block.

In some embodiments, the indication of skipping the transform and quantization process is excluded from the bitstream representation when a delta of the quantization parameters is not equal to zero.

In some embodiments, selectively signalling the indication of skipping the transform and quantization process is based on the quantization parameters for a luma component of the current video block.

5 Examples of the Disclosed Embodiments

FIG. 16 is a block diagram of a video processing apparatus 1600. The apparatus 1600 may be used to implement one or more of the methods described herein. The apparatus 1600 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 1600 may include one or more processors 1602, one or more memories 1604 and video processing hardware 1606. The processor(s) 1602 may be configured to implement one or more methods (including, but not limited to, methods 1500 to 1560 and 2100 to 2500) described in the present disclosure. The memory (memories) 1604 may be used for storing data and code used for implementing the methods and embodiments described herein. The video processing hardware 1606 may be used to implement, in hardware circuitry, some embodiments described in the present disclosure.

In some embodiments, the video coding methods may be implemented using an apparatus that is implemented on a hardware platform as described with respect to FIG. 16 .

Some embodiments of the present disclosure include making a decision or determination to enable a video processing tool or mode. In an example, when the video processing tool or mode is enabled, the encoder will use or implement the tool or mode in the processing of a block of video, but may not necessarily modify the resulting bitstream based on the usage of the tool or mode. That is, a conversion from the block of video to the bitstream representation of the video will use the video processing tool or mode when it is enabled based on the decision or determination. In another example, when the video processing tool or mode is enabled, the decoder will process the bitstream with the knowledge that the bitstream has been modified based on the video processing tool or mode. That is, a conversion from the bitstream representation of the video to the block of video will be performed using the video processing tool or mode that was enabled based on the decision or determination.

Some embodiments of the present disclosure include making a decision or determination to disable a video processing tool or mode. In an example, when the video processing tool or mode is disabled, the encoder will not use the tool or mode in the conversion of the block of video to the bitstream representation of the video. In another example, when the video processing tool or mode is disabled, the decoder will process the bitstream with the knowledge that the bitstream has not been modified using the video processing tool or mode that was disabled based on the decision or determination.

FIG. 17 is a block diagram that illustrates an example video coding system 100 that may utilize the embodiments of this disclosure. As shown in FIG. 17 , video coding system 100 may include a source device 110 and a destination device 120. Source device 110 generates encoded video data which may be referred to as a video encoding device. Destination device 120 may decode the encoded video data generated by source device 110 which may be referred to as a video decoding device. Source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130 a. The encoded video data may also be stored onto a storage medium/server 130 b for access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130 b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVM) standard and other current and/or further standards.

FIG. 18 is a block diagram illustrating an example of video encoder 200, which may be video encoder 114 in the system 100 illustrated in FIG. 17 .

Video encoder 200 may be configured to perform any or all of the embodiments of this disclosure. In the example of FIG. 18 , video encoder 200 includes a plurality of functional components. The embodiments described in this disclosure may be shared among the various components of video encoder 200. In some examples, a processor may be configured to perform any or all of the embodiments described in this disclosure.

The functional components of video encoder 200 may include a partition unit 201, a prediction unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205, and an intra prediction unit 206; a residual generation unit 207; a transform unit 208; a quantization unit 209; an inverse quantization unit 210; an inverse transform unit 211; a reconstruction unit 212; a buffer 213; and an entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, prediction unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform prediction in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated, but are represented in the example of FIG. 18 separately for purposes of explanation.

Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some examples, mode select unit 203 may select a combination of intra and inter prediction (CIIP) mode in which the prediction is based on an inter prediction signal and an intra prediction signal. Mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter prediction.

To perform inter prediction on a current video block, motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. Motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer 213 other than the picture associated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice.

In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may not output a full set of motion information for the current video. Rather, motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signalling techniques that may be implemented by video encoder 200 include advanced motion vector prediction (AMVP) and merge mode signalling.

Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.

Residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the prediction unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.

Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

FIG. 19 is a block diagram illustrating an example of video decoder 300 which may be video decoder 124 in the system 100 illustrated in FIG. 17 .

The video decoder 300 may be configured to perform any or all of the embodiments of this disclosure. In the example of FIG. 19 , the video decoder 300 includes a plurality of functional components. The embodiments described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the embodiments described in this disclosure.

In the example of FIG. 19 , video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, a reconstruction unit 306, and a buffer 307. Video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (FIG. 18 ).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used by video encoder 200 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

Motion compensation unit 302 may use some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 304 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transformation unit 305 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 302 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation/intra prediction and also produces decoded video for presentation on a display device.

In the present disclosure, the term “video processing” may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation, or coded representation, of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a video block may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream. Furthermore, during conversion, a decoder may parse a bitstream with the knowledge that some fields may be present, or absent, based on the determination, as is described in the above solutions. Similarly, an encoder may determine that certain syntax fields are or are not to be included and generate the coded representation accordingly by including or excluding the syntax fields from the coded representation.

FIG. 20 is a block diagram showing an example video processing system 2000 in which various embodiments disclosed herein may be implemented. Various embodiments may include some or all of the components of the system 2000. The system 2000 may include input 2002 for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8- or 10-bit multi-component pixel values, or may be in a compressed or encoded format. The input 2002 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc., and wireless interfaces such as Wi-Fi or cellular interfaces.

The system 2000 may include a coding component 2004 that may implement the various coding or encoding methods described in the present disclosure. The coding component 2004 may reduce the average bitrate of video from the input 2002 to the output of the coding component 2004 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 2004 may be either stored, or transmitted via a communication connected, as represented by the component 2006. The stored or communicated bitstream (or coded) representation of the video received at the input 2002 may be used by the component 2008 for generating pixel values or displayable video that is sent to a display interface 2010. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or DisplayPort, and so on. Examples of storage interfaces include serial advanced technology attachment (SATA), peripheral component interface (PCI), integrated drive electronics (IDE) interface, and the like. The embodiments described in the present disclosure may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.

FIG. 21 shows a flowchart of another exemplary method 2100 for video processing. The method 2100 includes determining 2102, at a sub-block level of a current video block comprising multiple sub-blocks, whether a coding mode is enabled for representing a corresponding sub-block in a bitstream representation, wherein, for a given sub-block with the coding mode enabled, the given sub-block is represented in the coded representation without applying a forward transform or the given sub-block is reconstructed from the coded representation without applying an inverse transform; and performing 2104, based on the determining, a conversion between the current video block of a video and the bitstream representation of the video.

In some embodiments for method 2100, wherein the coding mode includes a transquant bypass mode or a transform skip (TS) mode. In some embodiments for method 2100, wherein the current video block comprises a coding unit (CU), a transform unit (TU), or a prediction unit (PU), wherein the multiple sub-blocks are smaller in size than the CU, the TU, or the PU. In some embodiments for method 2100, wherein the current video block is associated with a chroma component, wherein the current video block is split into the multiple sub-blocks, and wherein the determining that the coding mode is enabled is performed for each sub-block. In some embodiments for method 2100, wherein the determining whether the coding mode is enabled is based on a coded information of a video block of a luma component corresponding to the current video block of the chroma component. In some embodiments for method 2100, wherein the multiple sub-blocks are split from the current video block based on a size of the current video block and a maximum size allowed for a transform process. In some embodiments for method 2100, wherein the coding mode is determined at least based on a size of the current video block and a maximum size allowed for the coding mode. In some embodiments for method 2100, wherein the determining whether the coding mode is applied to the sub-block is based on a syntax element included in the bitstream representation, and wherein the syntax element is associated with the given sub-block. In some embodiments for method 2100, wherein the syntax element indicates whether the TS mode or the transquant bypass mode is enabled for the sub-block.

FIG. 22 shows a flowchart of another exemplary method 2200 for video processing. The method 2200 includes determining 2202 that a conversion between a current video block of a video and a coded representation of the video is based on a first coding mode in which a lossless coding embodiment is used for representing the current video block in the coded representation; and performing 2204 the conversion, based at least on the determining, by disabling a luma mapping with chroma scaling (LMCS) process, wherein the disabling the LMCS process disables a performance of switching between samples in a reshaped domain and an original domain for the current video block in a case that the current video block is from a luma component or disables a scaling of a chroma residual of the current video block in case that the current video block is from a chroma component.

In some embodiments for method 2200, wherein the first coding mode in which the lossless coding embodiment is used includes a transquant bypass mode in which a transform and quantization process is not used on the current video block. In some embodiments for method 2200, wherein a residual of the current video block is coded in an original domain irrespective of whether a syntax element in the bitstream representation indicates that the reshaping and/or the scaling is enabled or disabled. In some embodiments for method 2200, wherein the syntax element is indicated in a slice or sequence level of the current video block. In some embodiments for method 2200, the method further comprises applying an inverse reshaping process to a prediction signal for the current video block to convert the prediction signal from a reshaped domain to an original domain, wherein the prediction signal is generated from reference samples within a tile, a slice, a tile group, or a picture of the current video block. In some embodiments for method 2200, wherein a prediction signal for the current video block is not converted from an original domain to a reshaped domain in a forward reshaping process in response to reference samples being within a picture that is different from that of the current video block. In some embodiments for method 2200, wherein the picture is a reference picture.

In some embodiments for method 2200, wherein the lossless coding embodiment of the first coding mode does not apply a transform operation to the current video block. In some embodiments for method 2200, wherein the first coding mode includes a transform skip (TS) mode. In some embodiments for method 2200, wherein a residual of the current video block is coded in an original domain irrespective of whether a syntax element in the bitstream representation indicates that the reshaping and/or the scaling is enabled or disabled. In some embodiments for method 2200, wherein an intra prediction mode is applied to the current video block, and wherein a prediction signal or reference samples used in the intra prediction mode for the current video block is mapped from a reshaped domain to an original domain.

In some embodiments for method 2200, wherein an intra block copy (IBC) mode is applied to the current video block, and wherein a prediction signal or reference samples used in the IBC mode for the current video block is mapped from a reshaped domain to an original domain. In some embodiments for method 2200, wherein a combined inter-intra prediction (CIIP) mode is applied to the current video block, and wherein a prediction signal or reference samples used in the CIIP mode for the current video block is mapped from a reshaped domain to an original domain. In some embodiments for method 2200, wherein a combined inter-intra prediction (CIIP) mode is applied to the current video block, and wherein a mapping of a prediction signal used in the CIIP mode for the current video block from an original domain to a reshaped domain is skipped. In some embodiments for method 2200, the method further comprises generating, in a palette mode and in an original domain, a palette table for the current video block. In some embodiments for method 2200, the method further comprises allocating a first buffer and a second buffer to the current video block, wherein the first buffer is configured to store a summation of a prediction signal and a residual signal, and wherein the second buffer is configured to store a reshaped summation that is obtained by mapping the summation of the prediction signal and the residual signal from an original domain to a reshaped domain.

In some embodiments for method 2200, the method further comprises allocating, to the current video block, a buffer that is configured to store a summation of a prediction signal and a residual signal in an original domain, wherein a reshaped summation is derived by mapping the summation of the prediction signal and the residual signal from the original domain to a reshaped domain. In some embodiments for method 2200, the method further includes applying, to the current video block, a coding mode that uses reference samples within a current title, a slice, a tile group, or a picture of the current video block.

FIG. 23 shows a flowchart of another exemplary method 2300 for video processing. The method 2300 includes performing 2302 a conversion between a current video block of a video and a bitstream representation of the video, wherein the bitstream representation conforms to a first format rule that specifies an order of occurrence of a first syntax element of a transquant bypass mode and one or more syntax elements of quantization parameters, wherein the bitstream representation conforms to a second format rule that specifies whether the first syntax elements and the one or more syntax elements are included in the coded representation, and wherein, in the transquant bypass mode, a transform and quantization process is not applied to the current video block during encoding or an inverse transform and an inverse quantization is not used during decoding of the coded representation for the current video block.

In some embodiments for method 2300, wherein the second format rule indicates that the first syntax element of the transquant bypass mode is included in the bitstream representation, and wherein the second format rule indicates that the first syntax element of the transquant bypass mode is included in the bitstream representation after signalling the one or more syntax elements of the quantization parameters. In some embodiments for method 2300, wherein the second format rule indicates that the first syntax element of the transquant bypass mode is included in the bitstream representation, and wherein the first format rule indicates that the first syntax element of the transquant bypass mode is included in the bitstream representation before signalling the one or more syntax elements of the quantization parameters. In some embodiments for method 2300, wherein the second format rule indicates that the bitstream representation excludes signalling of the one or more syntax elements of the quantization parameters and/or a second syntax element of a delta of quantization parameters in response to the transform and quantization process not being used on the current video block.

In some embodiments for method 2300, wherein the delta of quantization parameters is inferred to be zero. In some embodiments for method 2300, wherein the second format rule indicates that the first syntax element of the transquant bypass mode is excluded from the bitstream representation when a delta of the quantization parameters is not equal to zero. In some embodiments for method 2300, wherein the transform and quantization process is used on the current video block. In some embodiments for method 2300, wherein the second format rule indicates that the first syntax element of the transquant bypass mode is included in the bitstream representation based on the quantization parameters for a color component associated with the current video block. In some embodiments for method 2300, wherein the color component is a luma component.

FIG. 24 shows a flowchart of another exemplary method 2400 for video processing. The method 2400 includes performing 2402 a conversion between a current video block of a video segment of a video and a bitstream representation of a video, wherein the conversion is in conformance with a format rule that specifies an applicability relationship between an applicability of a transquant bypass mode and a luma mapped chroma scaling (LMCS) mode to the conversion of the current video block, wherein the format rule further specifies a syntax structure at the video segment level indicative of the applicability relationship, wherein, in the transquant bypass mode, a transform and quantization process is not used on the current video block, and wherein the LMCS mode comprises a performance of switching between samples in a reshaped domain and an original domain for the current video block in case that the current video block is from a luma component or a scaling of a chroma residual of the current video block in case that the current video block is from a chroma component.

In some embodiments for method 2400, wherein a syntax element that indicates whether the transquant bypass mode is enabled or disabled in the bitstream representation is based on a usage of the LMCS. In some embodiments for method 2400, wherein the syntax element for the transquant bypass mode is not included in the bitstream representation in response to the LMCS being applied to the current video block. In some embodiments for method 2400, wherein a syntax element of a usage of the LMCS in the bitstream representation is based on whether the transquant bypass mode is enabled or disabled.

FIG. 25 shows a flowchart of another exemplary method 2500 for video processing. The method 2500 includes performing 2502 a conversion between a current video block of a video and a bitstream representation of the video according to a first rule and a second rule, wherein the first rule specifies whether an inverse reshaping process is used during the conversion for generating decoded pixel values of the current video block by converting from a reshaped domain to an original domain, and wherein the second rule specifies an order in which the inverse reshaping process and a loop filtering process are applied for reconstruction of the current video block.

In some embodiments for method 2500, wherein the second rule specifies that the inverse reshaping process is applied before the loop filtering process. In some embodiments for method 2500, wherein the inverse reshaping process is not applied to the current video block when a transquant bypass mode is applied to the current video block, and wherein, in the transquant bypass mode, a transform and quantization process is not used on the current video block. In some embodiments for method 2500, wherein the inverse reshaping process is applied to the current video block when a coding mode other than a transquant bypass mode is applied to the current video block, and wherein, in the transquant bypass mode, a transform and quantization process is not used on the current video block.

From the foregoing, it will be appreciated that specific embodiments of the present disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed embodiments are not limited except as by the appended claims.

Embodiments of the subject matter and the functional operations described in the present disclosure can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing unit” or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example. As used herein, the use of “or” is intended to include “and/or”, unless the context clearly indicates otherwise.

While the present disclosure contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in the present disclosure in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in the present disclosure should not be understood as requiring such separation in all embodiments.

Only a few embodiments and examples are described and other embodiments, enhancements and variations can be made based on what is described and illustrated in the present disclosure. 

What is claimed is:
 1. A method of processing video data, comprising: determining, at a sub-block level of a current video block comprising multiple sub-blocks, whether a first coding mode is applied to each sub-block, wherein, for an encoding operation, the first coding mode does not apply a transform operation, or for a decoding operation, the first coding mode does not apply an inverse transform operation, and wherein the current video block is a coding unit, wherein the multiple sub-blocks are smaller in size than the coding unit; and performing, based on the determining, a conversion between the current video block of a video and a bitstream of the video.
 2. The method of claim 1, wherein the multiple sub-blocks are split from the current video block based on a size of the current video block and a first allowed maximum size for a transform process.
 3. The method of claim 1, wherein determining whether the first coding mode is applied to the sub-block is based on a first syntax element included in the bitstream, and wherein the first syntax element is associated with the sub-block.
 4. The method of claim 1, wherein whether the first coding mode is applied to the sub-block is determined at least based on a size of the sub-block and a second allowed maximum size for the first coding mode.
 5. The method of claim 4, wherein the first coding mode is applied to the sub-block at least under a condition that the size of the sub-block is smaller than or equal to the second allowed maximum size.
 6. The method of claim 4, wherein a single second syntax element that indicates the second allowed maximum size is included in the bitstream which is also used in a size constraint for a differential coding mode for a video block of a video region which also includes the current video block, and wherein in the differential coding mode, differences between quantized residuals derived with an intra prediction mode of the video block and predictions of the quantized residuals are included in the bitstream.
 7. The method of claim 6, wherein a third syntax element that indicates on/off control for the differential coding mode is included at a sequence parameter set (SPS) level of the bitstream under a conditional check of whether the first coding mode is allowed.
 8. The method of claim 1, wherein in the first coding mode, a quantization operation is also skipped in the encoding operation and an inverse quantization operation is also skipped in the decoding operation.
 9. The method of claim 1, wherein the conversion includes encoding the current video block into the bitstream.
 10. The method of claim 1, wherein the conversion includes decoding the current video block from the bitstream.
 11. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, at a sub-block level of a current video block comprising multiple sub-blocks, whether a first coding mode is applied to each sub-block, wherein, for an encoding operation, the first coding mode does not apply a transform operation, or for a decoding operation, the first coding mode does not apply an inverse transform operation, and wherein the current video block is a coding unit, wherein the multiple sub-blocks are smaller in size than the coding unit; and perform, based on the determining, a conversion between the current video block of a video and a bitstream of the video.
 12. The apparatus of claim 11, wherein the multiple sub-blocks are split from the current video block based on a size of the current video block and an allowed maximum size for a transform process.
 13. The apparatus of claim 11, wherein determining whether the first coding mode is applied to the sub-block is based on a first syntax element included in the bitstream, and wherein the first syntax element is associated with the sub-block.
 14. The apparatus of claim 11, wherein whether the first coding mode is applied to the sub-block is determined at least based on a size of the sub-block and an allowed maximum size for the first coding mode.
 15. The apparatus of claim 14, wherein the first coding mode is applied to the sub-block at least under a condition that the size of the sub-block is smaller than or equal to the allowed maximum size.
 16. The apparatus of claim 14, wherein a single second syntax element that indicates the allowed maximum size is included in the bitstream which is also used in a size constraint for a differential coding mode for a video block of a video region which also includes the current video block, and wherein in the differential coding mode, differences between quantized residuals derived with an intra prediction mode of the video block and predictions of the quantized residuals are included in the bitstream, and wherein a third syntax element that indicates on/off control for the differential coding mode is included at a sequence parameter set (SPS) level of the bitstream under the conditional check of whether a first coding mode is allowed.
 17. A non-transitory computer-readable storage medium storing instructions that cause a processorto: determine, at a sub-block level of a current video block comprising multiple sub-blocks, whether a first coding mode is applied to each sub-block, wherein, for an encoding operation, the first coding mode does not apply a transform operation, or for a decoding operation, the first coding mode does not apply an inverse transform operation, and wherein the current video block is a coding unit, wherein the multiple sub-blocks are smaller in size than the coding unit; and perform, based on the determining, a conversion between the current video block of a video and a bitstream of the video.
 18. The non-transitory computer-readable storage medium of claim 17, wherein determining whether the first coding mode is applied to the sub-block is based on a first syntax element included in the bitstream, and the first syntax element is associated with the sub-block, and wherein the first coding mode is applied to the sub-block at least under a condition that the size of the sub-block is smaller than or equal to a second allowed maximum size for the first coding mode.
 19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, at a sub-block level of a current video block of the video comprising multiple sub-blocks, whether a first coding mode is applied to each sub-block, wherein, for an encoding operation, the first coding mode does not apply a transform operation, or for a decoding operation, the first coding mode does not apply an inverse transform operation, and wherein the current video block is a coding unit, wherein the multiple sub-blocks are smaller in size than the coding unit; and generating the bitstream based on the determining.
 20. The non-transitory computer-readable recording medium of claim 19, wherein determining whether the first coding mode is applied to the sub-block is based on a first syntax element included in the bitstream, and the first syntax element is associated with the sub-block, and wherein the first coding mode is applied to the sub-block at least under a condition that the size of the sub-block is smaller than or equal to a second allowed maximum size for the first coding mode. 